The invention specifically relates to a double seat valve of the type, comprising a valve housing which has connectors for a first pipeline and a second pipeline, further comprising a first closing element and a first closing element seat which is assigned to the latter, wherein the first closing element is in seal-forming abutment, in its closed position, with the first closing element seat via at least one sealing element, and a second closing element which is spaced apart axially from the first closing element and a second closing element seat which is assigned to said second closing element, wherein the second closing element is, in its closed position, in seal-forming abutment with the second closing element seat via at least one sealing element, wherein the two closing elements can be independently of one another from their respective closing element seat, and wherein a leakage space is provided between the two closing elements.
Such a double seat valve is known from DE 10 2005 057 103 A1.
Double seat valves of the type specified above are used, for example, in the foodstuff industry for manufacturing products such as UHT-milk, yoghurt and the like.
In such double seat valves, stringent requirements are made of the reliable separation of the media which are conducted through the at least two pipelines. In their closed position, the two closing elements separate the two connectors on the inside of the housing in a sealed fashion in relation to one another, and in the common open position of the two closing elements the pipelines which are connected to the two connectors can communicate with one another via the interior of the housing.
A further significant requirement which is made of such double seat valves is that the closing elements, including their closing element seats and the leakage space which is located at least partially between the closing elements, can be thoroughly cleaned.
So that it is not necessary to switch off all the processes in a processing system in which such a double seat valve is used in order to clean the closing elements and the leakage space, which would reduce the productivity of such a processing system, it is desirable if the cleaning process is carried out, for example, by means of one of the two pipelines, while a product process continues to run in the other pipeline. For this purpose, the two closing elements can be lifted from their closing element seat independently of one another. “Lifting” is to be understood in such double seat valves as meaning that one of the two closing elements is moved from its closing element seat by a small stroke to such an extent that there is no longer a seal-forming abutment between the sealing element of this closing element and the associated closing element seat. In this context, the other closing element continues to be in abutment with its closing element seat in a seal-forming fashion. Through the pipeline and the connector which have the closing element which is lifted assigned to them it is then possible to introduce a cleaning medium, usually a cleaning fluid, between the closing element and the associated valve seat and into the leakage space so that the cleaning medium thoroughly flushes the closing element seat of the closing element which is lifted, and its sealing element and the leakage space.
The cleaning medium then runs outwards via the leakage space into the surroundings of the double seat valve.
The previously mentioned document DE 10 2005 057 103 A1 describes the problem that when the cleaning medium is introduced in accordance with the requirements of more recent standards an additional overpressure must not be formed in the leakage space, which overpressure could lead to the other closing element which is in the closed position being moved away from its closing element seat, with the result that cleaning medium could pass into the other pipeline in which a product process is currently running. In order to overcome this problem, said document proposes providing one of the closing elements with an obliquely positioned drainage section whose overall passage cross section is at least approximately as large as the opening cross section of the larger of the two connectors. This avoids the problem of the build up of overpressure in the leakage space as a result of an excessively small discharge of cleaning medium from the leakage space during cleaning.
However, this only solves the problem of avoiding an overpressure in the leakage space. A further requirement of more recent standards is that when the leakage space is acted on after one of the two closing elements has been lifted, there is no direct flow of cleaning medium against the at least one sealing element or the closing element seat of the other closing element which is in its closed position, because cleaning medium could then get into the other pipeline. The known double seat valve mentioned above does not meet this requirement. If, for example, the lower closing element of the known double seat valve is lifted and if cleaning medium under pressure is introduced into the gap between the closing element and its closing element seat and into the leakage space, the cleaning medium firstly impinges, owing to its essentially axial direction of flow at a high flow rate, on the closing element seat and the sealing element of the upper closing element which is in the closed position, as a result of which, owing to the impact pressure building up, cleaning medium can pass the sealing element of the upper closing element and penetrate the valve housing region through which a product medium is currently flowing.
In a double seat valve which is known from WO 2007/054 131 A1, the problem specified above is intended to be solved by virtue of the fact that, on the one hand, the closing element seat of one of the closing elements has a larger diameter than the closing element seat of the other closing element, with the result that the two closing element seats are offset radially from one another in a stepped fashion. Furthermore, one of the closing elements is provided, on a side facing the other closing element, with a flow-deflecting, concavely curved recess, by which the cleaning medium which penetrates the leakage space axially is deflected radially inward, with the result that the pressurized cleaning medium cannot be applied to the sealing element of the closing element which is in the closed position.
A disadvantage of this known double seat valve is, on the one hand, the complicated contouring of the inside of the housing in the region of the closing element seats and the complicated contouring of the closing elements which is intended to bring about deflection of the seat-cleaning flow of cleaning medium in order to avoid the closing sealing element being acted on directly. For this purpose, complex fluidic considerations are necessary in order to find the suitable contouring.